A host of organisms live in a human body. While all of these organisms benefit from living in a human body, not all of them live in symbiosis with their human host (i.e. are beneficial to their human host). Subsets of the organisms that live in a human body are simply parasitic and do not benefit the human host. A delicate balance between the symbiotic and parasitic organisms keeps the human body in a healthy state. However, when this delicate balance is compromised and the parasitic organisms grow to a critical population, they may cause adverse effects to their human host.